Ku-band missions are generally carried out using Gregorian antennae arranged on a satellite face that is oriented towards the Earth, commonly called the “Earth face”, and/or with single-offset antennae arranged on a lateral face of a satellite, provision often being made for both these types of antennae architectures in a single satellite. Because of placement constraints, these two reflector-based antennae architectures require different primary source geometries that are specific to each architecture. As a result, to ensure the various antennae provide their radiofrequency signal emission and reception functions, many different radiofrequency RF parts must be manufactured, tested and assembled, this possibly on the one hand creating problems with the reliability and sustainability of the RF, mechanical and thermal performance of the antenna and on the other hand increasing the cost and weight of the antennae.
A primary antenna source conventionally consists of a radiating element, for example a horn, fed by a radiofrequency RF chain essentially including a radiofrequency RF exciter. Known radiofrequency exciters conventionally consist of a plurality of different devices that allow sequentially on the one hand polarizations to be separated, then on the other hand emission and reception frequency bands to be separated.
A dual-linear-polarization radiofrequency exciter may for example consist of an asymmetrical two-orthogonal-arm orthomode transducer intended to separate two linear polarizations, called the horizontal H and vertical V polarizations, respectively, and two duplexers intended to separate, for each of the two linear polarizations, the frequency band of operation of the horn into two, emission and reception, sub-bands, respectively. This architecture employs a limited number of components to separate the frequency bands and polarizations, but can only be used when the emission and reception frequency bands are close to each other because its bandwidth is low. Furthermore, the use of an asymmetric OMT makes the antenna highly sensitive to propagation modes of higher order than the fundamental mode, this possibly degrading the radiofrequency performance of the antenna.
Alternatively, a dual-linear-polarization radiofrequency exciter may, for example, consist of a four-arm orthomode junction associated with recombining devices for separating the two, emission and reception, frequency bands and for sampling, then recombining, the two polarizations in the emission frequency band, the orthomode junction being connected to an orthomode transducer for separating the two polarizations of the reception frequency band. The use of a four-arm orthomode junction associated with recombining devices makes this architecture very complex, very bulky, and very difficult to integrate into Gregorian antennas.
Alternatively, a dual-linear-polarization radiofrequency exciter may, for example, consist of an asymmetrical orthomode junction comprising two orthogonal arms located in the same plane, for separating the two, emission and reception, frequency bands and the two polarizations in the emission frequency band, then an orthomode transducer for separating the two polarizations of the reception frequency band. This architecture has a low bulk, but a level of decoupling of the two polarizations comprised between −18 and −22 dB for the highest frequency band, this being very unsatisfactory for mono-beam coverage missions, which have a decoupling requirement of about −50 dB, and for multibeam coverage missions, which have a decoupling requirement of about −35 dB. This poor decoupling of the two linear polarizations is due to the asymmetric structure of the orthomode junction.